electric lines and rectifier stations are necessary. Consequently, the activ- 

 ities associated with placing electric lines may be required. 



Pipeline construction - moderately firm marsh soils. All of the actual 

 construction activities on the pipe itself - joining, welding, inspection, 

 cleaning, and wrapping - can be accomplished on a barge that is either station- 

 ary or moves along as each new section is added. Consequently, if a straight 

 line of pipe is to be laid in marsh soils where the ground is too soft to hold 

 heavy equipment, but where a ditch may be dug that will fill with water, the 

 pipe may be pushed from the barge and floated down the ditch for several 

 miles. Then it can be released from the floats and covered. Completely 

 assembled sections up to 76 cm (30 inches) in diameter and 24 km (15 mi) in 

 length can be laid by the push method (McGinnis et al., 1972). 



After the route has been planned and the right-of-way is obtained, sur- 

 veyors stake the route. They may travel by truck, marsh buggy, air boat, or 

 helicopter to reach all points along the survey line. It is very important 

 that the route to be pushed is straight, so the survey crew stakes the outside 

 limits of the canal to be dredged. 



A dragline, mounted on tracks (with timber mats) or placed on a marsh 

 buggy, is used to dig the pipeline ditch. The dredge usually moves away from 

 the site where the push barge is located. The spoil from the excavation is 

 placed on both sides of the ditch. In some ditch excavations, the dredge 

 operators have separated the marsh vegetation and upper soil from that dug in 

 deeper portions of the ditch. Thus, after the pipeline is in position, the 

 area can be refilled with the upper soil and remaining vegetation being replaced 

 last (True et al . , 1977). 



The pipeline canal is dug 1.2 to 1.8 m (4 to 6 ft) deep and 2.6 to 3.1 m 

 (8 to 10 ft) wide (Conner et al., 1976). When the dragline digs the canal, it 

 usually traverses the center of the area to be dug. This can lessen the 

 impact of compacting soil and vegetation that usually accompanies vehicle 

 movement in marshes. The dragline can be reached by small boat through the 

 canal. If the route to be dredged is long, care must be taken not to leave 

 trash and waste materials along the route. 



The area affected by ditching is about 9.1 m (30 ft) wide for small lines 

 (True et al., 1977) and wider for larger pipes. The depth of the ditch depends 

 on the size of pipe being laid; however, it is usual that 0.76 to 1.2 m (2.5 

 to 4 ft) remain between the top of the pipe and the soil level as prescribed 

 by Federal regulation. Marsh soil contains a large amount of water and organic 

 matter, and if piled up, may shrink and compact the soil below. Therefore, if 

 the spoil is to be used to backfill the trench, it must not remain out of the 

 water for more than a few days. Even if backfilling is done, the spoil will 

 not completely fill the flotation canal, although Willingham et al. (1975) 

 showed that backfilling promoted reestablishment of original conditions. 



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